Synthesis and in vitro antimicrobial evaluation of novel fluoroquinolone derivatives

Article abstract of DOI:10.1016/j.ejmech.2010.09.036

A series of 1-ethyl-6,8-difluoro-4-oxo-7(4-aryl piperazin-1-yl) 1,4-dihydro-quinoline-3-carboxylic acid derivatives (6a-f) and 1-ethyl-6,8-difluoro-4-oxo-7(4-piperidin-1-yl) 1,4-dihydro-quinoline-3- carboxylic acid derivatives (7a-e) were synthesized and evaluated for antibacterial and antifungal activities. The antimicrobial activities of the compounds were assessed by the microbroth dilution technique. The compounds were also evaluated for antifungal activity against Candida albicans (ATCC 90028) and Cryptococcous neoformans (ATCC 14116) pathogens. The preliminary in vitro evaluation studies revealed that some of the compounds have promising antimicrobial activities.

Full text of DOI:10.1016/j.ejmech.2010.09.036

European Journal of Medicinal Chemistry 45 (2010) 6101e6105
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
Synthesis and in vitro antimicrobial evaluation of novel fluoroquinolone
derivatives
Shanmugam Srinivasan a, Raja Mohmed Beema Shafreen b, Paramasivam Nithyanand b,
,
Paramasivam Manisankar a, Shunmugiah Karutha Pandian b
*
a Department of Industrial Chemistry, Alagappa University, Karaikudi-630 003, Tamil Nadu, India
b Department of Biotechnology, Alagappa University, Alagappapuram, Karaikudi-630 003, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 1-ethyl-6,8-difluoro-4-oxo-7(4-aryl piperazin-1-yl) 1,4-dihydro-quinoline-3-carboxylic acid
derivatives (6aef) and 1-ethyl-6,8-difluoro-4-oxo-7(4-piperidin-1-yl) 1,4-dihydro-quinoline-3-carbox-
ylic acid derivatives (7aee) were synthesized and evaluated for antibacterial and antifungal activities.
The antimicrobial activities of the compounds were assessed by the microbroth dilution technique. The
compounds were also evaluated for antifungal activity against Candida albicans (ATCC 90028) and
Cryptococcous neoformans (ATCC 14116) pathogens. The preliminary in vitro evaluation studies revealed
that some of the compounds have promising antimicrobial activities.
Received 19 January 2010
Received in revised form
15 September 2010
Accepted 16 September 2010
Available online 22 September 2010
Keywords:
Fluoroquinolones
Antibacterial
Ó 2010 Elsevier Masson SAS. All rights reserved.
Antifungal
Structure activity relationship
1. Introduction
progress in this field for the discovery of several synthetic anti-
fungal agents such as fluconazole, ketoconazole and miconazole,
The prevalence of newly emerging virulence traits and drug
resistance of the pathogens towards the antibiotics have become
a serious problem. Thus the design of new agents active against the
resistant organisms is of critical importance. The new generations
of Fluoroquinolone achieved significant improvement in potency,
spectrum and physicochemical properties [1e5]. The structur-
eeactivity relationship (SAR) studies revealed that, the fluorine
atom and the 1-alkyl,1,4-dihydro-4-oxoquinoline-3-carboxylic acid
skeleton of Fluoroquinolone are responsible for potency repre-
sented in binding with type-II topoisomerase enzymes, DNA gyrase
and topoisomerase IV. In addition, it is believed that the 6-fluoro
and 7-piperazinyl groups are responsible for the broad spectrum
and antipseudomonal activities of Fluoroquinolone [6e10]. More-
over, it is clear that chemical modifications at C-7 are suitable for
controlling of the pharmacokinetic properties and hence changes in
the cell permeability of these antibiotics [11e13]. The third gener-
ation Fluoroquinolone such as lomefloxacin and fleroxacin exhibi-
ted longer duration of action, while sparfloxacin and tosufloxacin
revealed higher potency against Gram-positive cocci and anaerobic
bacteria than the earlier members [14,15]. There has been much
including amphotericin B for treatment of the life-threatening
fungal infections [16e19]. Antifungal agents, polyenes and azoles
are available for the treatment of serious and life-threatening
fungal infections, mainly caused by Candida albicans and Ase-
pergillus fumigatus [20]. Despite advances in antifungal therapies,
many problems still remains to be solved. Also the use of azoles,
such as fluconazole, ketoconazole and miconazole, has resulted in
clinically resistant strains of Candida sp. [21,22].
In light of these considerations, we report the synthesis of two
series of Fluoroquinolone derivatives. The first series describe the
synthesis of various N-aryl substitued piperazine derivatives at C-7
position of 1-ethyl-6,8-difluoro-4-oxo-1,4-dihydro-quinoline-3-
carboxylic acid(6aef) asproposed inFig.1. The second series describe
synthesis of various piperidyl derivatives at C-7 position of 1-ethyl-
6,8-difluoro-4-oxo-1,4-dihydro-quinoline-3-carboxylic acid (7aee)
as proposed in Fig. 2. All the novel derivatives were screened for their
antimicrobial activity and their results are discussed.
2. Chemistry
Herein we report the synthesis, characterization and novel fluo-
roquinolone derivatives of N-aryl, N-benzyl, substituted N-aryl
piperazine and N-piperadine. The key intermediate 6,7,8-trifluoro-1-
ethyl-4-oxo-1,4-dihydro-quinoline-3-carboxylic acid (5) was
* Corresponding author. Tel.: þ91 4565 225215; fax: þ91 4565 225202.
E-mail address: sk_pandian@rediffmail.com (S.K. Pandian).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.09.036

6102
S. Srinivasan et al. / European Journal of Medicinal Chemistry 45 (2010) 6101e6105
Fig. 1. General structure and numeration of N-substituted aryl piperazine derivatives
(6aef).
prepared as described earlier (Scheme 1). The additioneelimination
reaction of 2,3,4-trifluoroaniline (1) to diethylethoxymethylene mal-
onate gives the corresponding enamino ester (2); thermal cyclization
of this compound, followed by N-alkylation using ethyl iodide leads to
the formation of quinolone ethyl ester (4). Hydrolysis of ester gives free
carboxylic acid (5). The C-7 fluorine atom of (5) was then allowed to
react with 1-(2-fluorophenyl) piperazine, 1-(4-fluorophenyl) pipera-
zine, 1-(2-cyanophenyl) piperazine, 1-benzylpiperazine, 1-phenyl-
piperazine, 1-(2,3-dichlorophenyl) piperazinein pyridine was then,
heated to 80 ꢀC which gave N-substituted piperazine fluoroquinolone
derivatives 6aef in good to excellent yields via nucleophilic substi-
tutions as depicted in Scheme 2. The compounds 7aee were prepared
from the same intermediate 5 by nucleophilic aromatic substitution
reaction with 4-(methyl amino) piperidine, 4-methylpiperidine,
4-piperidine methanol, 4-piperidinopiperidine, 4-bromo piperidine
in N-methyl pyrrolidine solvent as outlined in Scheme 3.
Scheme 1. Synthesis of 6,7,8-trifluoro-1-ethyl-oxo-1, 4-dihydro-quinoline-3-carbox-
ylic acid. Reagents and condition: (a) diethyl ethoxy methylene malonate, 100e120 ꢀC,
2 h (b) Diphenyl ether 250 ꢀC (c) Etl, K2CO3, DMF, Reflux, 10 h (d) Conc. HCl, Acetic acid.
4. Results and discussion
The structure of the synthesized compounds was confirmed by
spectral data (IR,1H NMR EIMS and 13C NMR) and presented inTable
1 (Supplementary material S1). The antimicrobial activity of the 11
novel Fluoroquinolone derivatives (6aef) and (7aee) was assessed
in comparison with quinolone ciprofloxacin, against the Gram-
positive, Gram-negative and fungal pathogens using a conventional
agar dilution procedure and the results are summarized in Table 2.
The antibacterial data suggest that the Gram-positive organisms
S. salivarius and S. mitis and the Gram-negative K. pneumoniae and
P. mirabilis are susceptible to all the 11 novel derivatives (6aef) and
(7aee). The most active compounds against S. boydii are 6f, 7a, 7d
and 7e. The compound 7c was showing a potent antibacterial
3. Pharmacology
activity against the Vibrio sp. tested (MIC ¼ 1e1.25
Compared to ciprofloxacin (MIC ¼ 2.5 g/mL), the fluoroquinolone
derivative 7e is known to have enhanced antibacterial activity
against all the Gram-positive test organisms used (MIC ¼ 1 g/mL).
Among the compounds, 7c exhibited the strongest antibacterial
activity (MIC ¼ 0.5e2 g/mL) against the susceptible organisms.
mg/mL).
m
The in vitro antimicrobial activity of all the synthesized
compounds was tested against the Gram-positive [Bacillus subtilis
ATCC 11774, Staphylococcus aureus ATCC 11632, Staphylococcus
epidermidis ATCC 12228, Streptococcus salivarius ATCC 13419,
Streptococcus sanguinis ATCC 10556 and Streptococcus mitis ATCC
6249], Gram-negative [Aeromonas hydrophila ATCC 7966, Vibrio
alginolyticus ATCC 17749, Vibrio parahaemolyticus ATCC 17802,
Klebsiella pneumoniae ATCC 10031, Proteus mirabilis ATCC 7002,
Proteus vulgaris ATCC 49132, Pseudomonas aeruginosa ATCC 10145,
Salmonella paratyphi A ATCC 9150 and Shigella boydii ATCC 9207]
and fungal [C. albicans ATCC 90028, Cryptococcous neoformans ATCC
14116] pathogens. Antimicrobial susceptibility test was assayed
using 96 well microtiter plates. Muller Hinton broth (MHB) was
used to culture bacteria and Sabouraud’s broth (SDB) was used to
cultivate fungal isolate. The bacterial and fungal suspensions were
added to the MHB and SDB respectively supplemented with varying
concentrations of the test compounds, incubated at 37 ꢀC for
18e24 h. Following incubation, microtiter plates were read visually
with the aid of a reading mirror and spectrophotometrically set at
450 nm. The MIC was recorded as the lowest concentration that
produced complete suppression of visible growth.
m
m
The MICs of some of the newly synthesized compounds such as 7a,
7c, 7e and 6f against the fungal pathogens are much lower when
compared to the MIC of Norflaxacin (Table 2). The antifungal test
results revealed that the N-aryl substituted piperazines (6f) and N-
aryl substituted piperidines (7c) are found to be potent inhibitors
against both the fungal species tested. The overall antimicrobial
data indicated that the newly synthesized compounds 7aec have
a strong and better activity against the test organism than the
reference quinolones. Most of the test organisms used are human
pathogens capable of causing various infections in human.
Substituting N-aryl piperazines and piperidines moiety on the C-7
position of 1-ethyl-6,8-difluoro-4-oxo-1,4-dihydro-quinoline-3-
carboxylic acid produces a series of novel fluoroquinolone deriva-
tives. Most of the new compounds demonstrated high in vitro
antibacterial activity against test organisms which were more
potent than those ciprofloxacin and norfloxacin. These compounds
may serve as useful lead molecules for new antibiotic drug
discoveries.
5. Experimental section
Solvents for chromatography and other reagents were obtained
from commercial sources and were used as such without any
further purification unless specified. The melting points are recor-
ded on Buchi-535 apparatus and are uncorrected. The 1H NMR
spectra were obtained using a 400 MHz Varian Gemini spectrom-
eter using tetramethylsilane as internal standard. Infrared spectra
were recorded using a PerkineElmer model 1640 instrument. Mass
Fig. 2. General structure and numeration of N-substituted piperadine derivatives
(7aee).

S. Srinivasan et al. / European Journal of Medicinal Chemistry 45 (2010) 6101e6105
6103
Scheme 2. Synthesis of N-substituted aryl piperazine fluoroquinolone derivatives (6aef).
spectra were recorded on an MS Engine-HewlettePackard model
5989 at DIP 20 eV. Yields are of purified products and are not
optimized.
J ¼ 7.3 Hz, NeCH2), 3.5 (s, 4H of piperazine), 3.2 (s, 4H of pipera-
zine), 1.5 (t, 3H, J ¼ 6.8 Hz, NeCH2eCH3); ESMS m/z (% of relative
abundance): 432.1 (M þ 1).
5.2.2. 1-Ethenyl-6,8-difluoro-7-(4-fluorophenyl-1-piperazinyl)-4
(1H)-oxoquinoline-3-carboxylic acid (6b)
5.1. Procedure for the synthesis of 1-ethenyl-6,7,8-trifluoro-4-oxo-
1,4-dihydro-quinoline-3-carboxylic acid (5)
A yellow solid; yield (88%); mp 236e242 ꢀC; IR (KBr) cmꢁ1; 3053
(eOeH stretching of carboxylic acid), 1720 (pC]O stretching of
carboxylic acid), 1618 (pC]O stretching of conjugated ketone),
A mixture of 2,3,4-trifluoroaniline 1 (20 g, 2.013 mol) and
diethyl ethoxymethylenemalonate (44 g, 2.03 mol) was heated at
110e120 ꢀC in an oil bath for 2 h, the resulting EtOH was eliminated
by distillation. Then, the mixture was cooled and the obtained
residue was directly refluxed for 6 h with diphenyl ether (350 ml).
After the solution was cooled, the resulting precipitate was filtered
off to obtain crude product which was refluxed in potassium
carbonate (34.4 g, 25 mol) and ethyl iodide (50 mol). After 10 h, the
inorganic material was filtered off and washed with ethanol. Then,
the filtrate was cooled to yield the ethyl ester 4 (15 g, 50%) as
a white solid. The ethyl ester 4 was refluxed in the mixture of acetic
acid: hydrochloric acid (2:1 ratio) for 4 h. Dilution with water and
filtration gave the title compound as a crude material. Then the
compound was purified by column chromatography (CHCl3/
hexane/2-propanol 4:5:1) to get the title compound as a white solid
with 70% yield. Mp 211e213 ꢀC; IR (KBr) cmꢁ1: 3047 (eOeH
stretching of carboxylic acid), 1722 (pC]O stretching of carboxylic
acid), 1703 (pC]O stretching of conjugated ketone), 1234 (CeN
1234 (CeN stretching); 1H NMR (400 MHz,
d, ppm, CDCl3:CH3OD):
d
8.68 (s 1H CH]CeCOOH), 7.98 (dd, 1H, AreH, J ¼ 9.8 Hz, C-5
proton), 7.0 (m, 1H, AreH), 4.5 (dd, 2H, J ¼ 3.4 Hz, NeCH2), 3.50 (s,
4H of piperazine), 3 (s, 4H of piperazine), 1.5 (t, 3H, J ¼ 5.9 Hz,
NeCH2eCH3); ESMS m/z (% of relative abundance): 432.1 (M þ 1).
5.2.3. 1-Ethenyl-6,8-difluoro-7-(2-cyanolphenyl-1-piperazinyl)-4
(1H)-oxoquinoline-3-carboxylic acid (6c)
A yellow solid; yield (89%); mp 252e259 ꢀC; IR (KBr) cmꢁ1; 2223
(nitrile stretching), 3045 (eOeH stretching of carboxylic acid), 1722
(pC]O stretching of carboxylic acid), 1622 (pC]O stretching of
conjugated ketone); 1H NMR (400 MHz,
d
, ppm, CDCl3:CD3OD):
d
8.78 (s 1H, CH]CeCOOH), 8.08 (m, 1H, AreH, C-5 proton), 7.68
(m, 2H, AreH), 7.18 (m, 2H, AreH), 4.48 (q, 2H, J ¼ 3.5 Hz, NeCH2),
4.68 (m, 2H of piperazine), 3.68 (s, 4H of piperazine), 3.2 (s, 4H of
piperazine), 1.68 (m, 2H of piperazine), 1.5 (m, 3H, NeCH2eCH3);
ESMS m/z (% of relative abundance): 439.12 (M þ 1).
stretching,); 1H NMR (400 MHz,
d, ppm, CDCl3:CD3OD): d, ppm, 8.8
(s, 1H, CH]CeCOOH), 8.2 (dt, 1H, AreH), 4.6 (q, 2H, J ¼ 4 Hz,
NeCH2), 1.6 (t, 3H, J ¼ 7.4 Hz, NeCH2eCH3); ESMS m/z (% of relative
abundance): 272.1 (M þ 1), 294 (M þ Na).
5.2.4. 1-Ethenyl-6,8-difluoro-7-(N-benzyl-1-piperazinyl)-4(1H)-
oxoquinoline-3-carboxylic acid (6d)
A yellow solid; yield (77%); mp 232e235 ꢀC; IR (KBr) cmꢁ1; 3084
(eOeH stretching of carboxylic acid), 1720 (pC]O stretching of
carboxylic acid), 1624 (pC]O stretching of conjugated ketone); 1H
5.2. General procedure for the synthesis of N-substituted aryl
piperazines (6aef)
NMR (400 MHz,
d, ppm, CDCl3:CD3OD): d 8.68 (s 1H, CH]
A mixture of 5 (1.0 mmol) and N-aryl piperazine (1.2 mmol) in
10 ml pyridine was heated at 80 ꢀC for 40 min. The reaction mixture
was concentrated under reduced pressure. The residue was diluted
with water and extracted with CHCl3. The organic layer was dried
and concentrated to leave a crude product, which was recrystal-
lized from the acetonitrile 70e82% yield.
CeCOOH), 7.9 (d, 1H, AreH, J ¼ 2 Hz; J ¼ 9.7 Hz), 7.48 (m, 5H, AreH),
4.58 (dd, 2H, J ¼ 3.4 Hz, NeCH2), 3.7 (s, 2H of piperazine) 3.4 (s, 2H
of piperazine), 1.58 (t, 3H, J ¼ 6.3 Hz, NeCH2eCH3), 2.68 (m, 4H,
piperazine); ESMS m/z (% of relative abundance): 428.1 (M þ 1).
5.2.5. 1-Ethenyl-6,8-difluoro-7-(N-phenyl-1-piperazinyl)-4(1H)-
oxoquinoline-3-carboxylic acid (6e)
5.2.1. 1-Ethenyl-6,8-difluoro-7-(2-fluorophenyl-1-piperazinyl)-4
(1H)-oxoquinoline-3-carboxylic acid (6a)
A yellow solid; yield (85%); mp 232e237 ꢀC; IR (KBr) cmꢁ1; 3051
(eOeH stretching of carboxylic acid), 1720 (pC]O stretching of
carboxylic acid), 1618 (pC]O stretching of conjugated ketone),
A yellow solid; yield (87%); mp 235e242 ꢀC; IR (KBr) cmꢁ1; 3043
(eOeH stretching of carboxylic acid), 1720 (pC]O stretching of
carboxylic acid), 1622 (pC]O stretching of conjugated ketone),
1232 (CeN stretching); 1H NMR (400 MHz,
d, ppm, CDCl3): d 8.7 (s,
1234 (CeN stretching); 1H NMR (400 MHz,
d
, ppm, DMSO);
8.98 (s 1H, CH]CeCOOH), 7.98 (d, 1H, J ¼ 11.7 Hz,
AreH, C-5 proton), 7.2 (m, 3H, AreH), 7.0 (m,1H, AreH), 4.60 (q, 2H,
d 15.4 (s
1H, CH]CeCOOH), 7.9 (dd, 1H, AreH, J ¼ 2.0 Hz, J ¼ 10.2 Hz), 7.3
(m, 2H, AreH), 7.0 (m, 2H, AreH), 6.98 (m, 1H, AreH), 4.5(dd, 2H,
J ¼ 3.4 Hz, NeCH2), 3.6 (s, 4H of piperazine), 3.5 (s, 4H of
1H, COOH),
d
Scheme 3. Synthesis of substituted piperadine fluoroquinolone derivatives (7aee).

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S. Srinivasan et al. / European Journal of Medicinal Chemistry 45 (2010) 6101e6105
Table 1
13C NMR spectra of N-substituted aryl piperazine derivatives (6aef) and N-substituted piperadine derivatives (7aee).
Compound COOH C-4
C-6 and C-8 C-5
C-10
C-2
C-3
C-40 C-20 and C-60 C-50 C-30 C-100
C-200 Substituent ‘R’
6a
6b
6c
166.23 149.26 129.20
167.41 150.35 129.43
165.89 148.86 128.87
127.18 108.74 108.36 108.22
127.23 108.19 107.91 107.68
126.54 107.21 106.96 106.90
e
e
e
54.73
54.68
53.82
54.31 53.28
54.22 53.15
53.40 52.41
50.74 16.38 CeF (130.12) and Other Ph C (128.05)
50.71 16.30 CeF (132.81) and Other Ph C (128.25)
49.96 15.97 CeCN (118.64) and Other Ph C (115.22),
CN (110.48)
6d
6e
6f
166.64 149.91 129.18
166.52 149.74 129.22
166.14 149.56 129.15
127.27 108.48 108.17 108.02
127.72 108.34 108.02 107.95
127.67 108.56 108.25 108.11
e
e
e
54.68
54.45
54.22
54.47 53.44 5089
16.31 Ph (128.31) and AreC (63.08)
54.20 53.20
53.81 52.94
50.82 16.02 Ph 128.26
50.69 16.25 CeCl (134.17) and other Ph
C (129.03)
7a
7b
7c
7d
7e
166.21 149.62 129.47
164.96 148.22 128.91
166.72 149.94 129.42
166.25 149.47 129.13
166.18 149.11 129.08
127.51 108.22 108.01 107.86 25.61 54.36
126.42 107.68 107.40 107.21 24.14 53.81
127.33 108.15 107.85 107.67 25.34 54.64
127.62 108.36 108.35 107.92 25.59 54.68
127.45 108.47 108.12 107.98 25.28 54.75
53.94 52.91
53.36 52.29
54.23 53.18
54.26 53.25
54.33 53.36
50.25 16.34 CeNH (32.54)
49.87 15.98 C H (12.31)
50.33 16.28 CeO (51.46)
50.24 16.15 CeCN 34.14 and other C 20.08
50.27 16.37
e
piperazine), 1.5 (t, 3H, J ¼ 6.3 Hz, NeCH2eCH3); ESMS m/z (% of
relative abundance): 414.1 (M þ 1).
DMSO): d 9.0 (s, 1H, CH]CeCOOH), 7.9 (dd, 1H, AreH,
J ¼ 12.2 Hz), 4.56 (q, 2H, J ¼ 3.4 Hz, NeCH2), 3.5 (m, 2H of
piperadine), 3.2 (m, 2H, piperadine), 2.8 (m, 2H of piperadine),
2.1 (s, 3H, NHeCH3), 1.8 (m, 2H of piperadine), 1.8 (m, 1H of
piperadine), 1.5 (t, 3H, J ¼ 6.8 Hz, NeCH2eCH3); ESMS m/z (% of
relative abundance): 366.1 (M þ 1).
5.2.6. 1-Ethenyl-6,8-difluoro-7-(2,3-dichloro-phenyl-1-
piperazinyl)-4(1H)-oxoquinoline-3-carboxylic acid (6f)
A yellow solid; yield (80%); mp 262e266 ꢀC; IR (KBr) cmꢁ1; 3043
(eOeH stretching of carboxylic acid), 1722 (pC]O stretching, of
carboxylic acid), 1620 (pC]O stretching of conjugated ketone),
5.3.2. 1-Ethenyl-6,8-difluoro-7-(4-methyl -piperidinyl)-4(1H)-
oxoquinoline-3-carboxylic acid (7b)
1232 (CeN stretching); 1H NMR (400 MHz,
d, ppm, DMSO): d 8.9 (s
1H, CH]CeCOOH), 7.9 (d, 1H, J ¼ 12.2 Hz, AreH), 7.1 (m, 2H, AreH),
7.3 (m, 1H, AreH), 4.6 (dd, 2H, J ¼ 3.9 Hz, NeCH2), 3.5 (m, 6H of
piperazine), 3.2 (m, 2H of piperazine), 1.5 (t, 3H, J ¼ 6.4 Hz,
NeCH2eCH3); ESMS m/z (% of relative abundance): 482.1 (M þ 1).
A yellow solid; yield (80%); mp 234e238 ꢀC; IR (KBr) cmꢁ1; 3053
(eOeH stretching of carboxylic acid), 1720 (pC]O stretching of
carboxylic acid), 1622 (pC]O stretching of conjugated ketone),
1211 (CeN stretching); 1H NMR (400 MHz
d, ppm, CDCl3:CD3OD):
d
8.7 (s 1H, CH]CeCOOH), 7.9 (d, 1H, J ¼ 1.9 and 9.8 Hz), 4.5 (dd,
2H, J ¼ 3.5 Hz, NeCH2), 3.5 (m, 2H of piperadine), 3.2 (dt, 2H of
piperadine), 1.8 (dd, 2H of piperadine, J ¼ 2.0 Hz), 1.4 (dq, 2H of
piperadine), 1.0 (d, 3H, J ¼ 6.4 Hz, CH3 of piperadine), 1.6 (t, 3H,
NeCH2eCH3), 1.7 (m, 1H of piperadine); ESMS m/z (% of relative
abundance): 351.1 (M þ 1).
5.3. General procedure for the synthesis of substituted piperidines
(7aee)
A mixtureof5 (1.0 mmol) and piperidinylcompounds(1.2 mmol)
in 10 ml N-methyl pyrrolidine was heated at 110e120 ꢀC for 4 h. The
reaction mixture was concentrated under reduced pressure. The
residue was diluted with water and filtered off the crude compound.
The crude product, which was recrystallized from the mixture of
CHCl3:methanol mixture to give 70e82% yield.
5.3.3. 1-Ethenyl-6,8-difluoro-7-(4-hydroxymethyl-piperidinyl)-4
(1H)-oxoquinoline-3-carboxylic acid (7c)
A yellow solid; yield (80%); mp 226e230 ꢀC; IR (KBr) cmꢁ1; 3485
(eOeH stretching of eCH2OH group), 3041 (eOeH stretching of
carboxylic acid), 1712 (pC]O stretching of carboxylic acid), 1622
(pC]O stretching of conjugated ketone), 1247 (CeN stretching); 1H
5.3.1. 1-Ethenyl-6,8-difluoro-7-(4-methyl amino-piperidinyl)-4
(1H)-oxoquinoline-3-carboxylic acid (7a)
A yellow solid; yield (82%); mp 245e246 ꢀC; IR (KBr) cmꢁ1
;
NMR (400 MHz d, ppm, CDCl3:CD3OD): d 14.8 (s, 1H, COOH), 8.6 (s,
3415 (eOeH stretching of carboxylic acid), 1714 (pC]O stretch-
ing of carboxylic acid), 1635 (pC]O stretching of conjugated
1H, CH]CeCOOH), 7.9 (dd, 1H, J ¼ 2.0 and 9.8 Hz), 4.5 (q, 2H,
J ¼ 3.4 Hz, NeCH2), 3.6 (d, 2H, J ¼ 6.3 Hz, CH2OH), 3.5 (d, 2H of
ketone), 1244 (CeN stretching); 1H NMR (400 MHz,
d, ppm,
Table 2
In vitro antibacterial and antifungal activity of synthesized novel series of fluoroquinolone derivatives and standard quinolones (MIC mg/mL).
Test organism
Ciprofloxacin
Norfloxacin
6a
6b
6c
6d
6e
6f
7a
7b
7d
7c
7e
S. boydii (9207)
2.50
3.00
2.00
8.00
3.00
6.00
1.50
4.00
0.50
1.50
1.00
1.50
4.00
2.50
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
312.50
4.88
2.00
1.50
nil
1.50
2.50
5.00
1.50
nil
nil
1.25
nil
1.00
nil
1.50
nil
2.00
nil
nil
1.50
2.50
1.25
1.50
nil
nil
2.50
nil
1.50
nil
1.50
nil
2.00
nil
nil
1.50
1.00
2.50
1.00
1.50
nil
1.50
nil
2.50
nil
1.50
nil
nil
1.50
1.50
nil
1.50
nil
1.50
1.00
1.00
nil
nil
nil
2.50
nil
1.50
nil
nil
nil
nil
nil
1.50
1.50
2.00
nil
1.00
0.50
1.00
1.25
2.50
5.00
1.25
5.00
nil
5.00
1.00
2.50
nil
1.00
2.00
2.50
0.50
1.25
1.25
5.00
5.00
1.00
1.25
2.50
2.50
2.00
2.50
nil
nil
nil
nil
1.00
0.50
nil
2.50
1.25
1.25
2.50
1.00
nil
0.50
1.00
1.00
1.25
1.25
1.25
2.50
5.00
1.50
1.00
1.25
1.25
2.00
2.50
1.00
1.50
nil
5.00
2.50
5.00
5.00
nil
A. hydrophila (7966)
V. alginolyticus (17749)
V. parahaemolyticus (17802)
P. vulgaris (49132)
P. mirabilis (7002)
K. pneumonia (10031)
S. paratyphi A (9150)
P. aeruginosa (10145)
B. subtilis (11774)
1.50
1.00
2.50
1.50
nil
nil
5.00
nil
2.50
nil
1.00
nil
nil
nil
5.00
1.00
1.00
nil
1.50
413.40
nil
nil
2.50
5.00
2.50
nil
1.00
415.00
1.03
S. aureus (11632)
2.50
2.50
nil
2.50
nil
S. salivarius (13419)
S. sanguinis (10556)
S. mitis (6249)
C. albicans (90028)
C. neoformans (14116)
5.00
108.00
2.17
183.10
4.19
nil
nil
nil
nil
1.82
nil
nil

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1244 (CeN stretching); 1H NMR (400 MHz,
d, ppm, CDCl3): d 8.6 (s
1H, CH]CeCOOH), 7.9 (d, 1H, J ¼ 2.0 and 9.8 Hz, AreH), 4.5 (dd, 2H,
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COOH), 8.9 (s 1H, CH]CeCOOH), 7.9 (d, 1H, J ¼ 1.9 and 10.3 Hz,
AreH),1.4 (t, 3H, J ¼ 6.9 Hz, NeCH2eCH3), 4.6 (m,1H of piperadine),
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Acknowledgement
The financial support provided to RMBS by DBT (Grant No. BT/
BI/25/001/2006) is gratefully acknowledged.
Appendix. Supplementary material
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